This invention relates to a method and apparatus for scheduling packets in an orthogonal frequency division multiple access (OFDMA) system. More particularly, the presently described embodiments relate to a scheduling system whereby packets are prioritized based on packet delay information.
While the invention is particularly directed to the art of scheduling packets in an OFDMA environment, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in other environments where prioritizing packets is advantageous.
By way of background, OFDMA systems are utilized as an air interface in fourth generation (4G) systems for wireless communication. Where flexibility in providing bandwidth for multiple users is desired, OFDMA provides a solution. OFDMA requires that users be assigned to certain bandwidth designations, regardless of the needs of the users at a particular moment. So, the flexibility resides in the ability to serve more users at a given time. Scheduling the users on the system becomes important to manage the system effectively.
However, OFDMA systems have the capability to be used to transmit voice-over-internet-protocol (VOIP) calls. To minimize control signaling overhead, including signaling messages in OFDMA systems, an approach called persistent assignment is supported in Ultra Mobile Broadband (UMB) standard for VOIP applications. Persistent assignment is particularly useful where the number of simultaneously scheduled users in a sector is very high.
One implementation of persistent assignment scheduling is that, once a voice-over IP user begins a talk spurt, and is allocated with a resource unit, the user maintains the same resource unit until the end of the talk spurt. Also, the transmission format remains the same for all of the data transmitted until a persistent assignment expires.
To explain, with reference to FIG. 1, a frequency spectrum 10 is shown in an OFDMA system. As shown, the frequency spectrum includes pilot sub-carriers 12 as well as user data sub-carriers 14 and 16. For completeness, the guard bands 18 are also shown. It should be appreciated that the data sub-carriers or interlaces, are used to transmit data in the system. If persistent assignment is used, these sub-carriers are consistently used for a user during a, for example, a talk spurt.
A disadvantage of prior art of implementing voice-over IP in OFDMA systems is that the system does not take into account of packet delay when scheduling a new user. As a result, quality of service may suffer because higher priority calls may have to wait while the resources are used in a fixed manner in the OFDMA system.
As such, it is desirable to have a system whereby packets can be scheduled on a more efficient basis.
The present invention contemplates a new and improved that resolves the above-referenced difficulties and others.